In recent years, a portable radio apparatus typified by a mobile telephone has expanded in functionality as multiple functions and an apparatus installing functions other than telephone communication functions, such as a digital TV broadcast reception function and a GPS (Global Positioning System) function, (which will be hereinafter referred to as “multifunctional portable radio apparatus”) has become widespread. Of such multifunctional portable radio apparatuses, an apparatus installing the digital TV broadcast reception function requires a wide-band antenna system covering a continuous wide digital TV broadcast frequency band (470 MHz to 770 MHz: Ratio band 48%). An apparatus installing other various communication functions (which will be hereinafter referred to as “applications”) than telephone communication functions requires a wide-band antenna system operating covering the operation frequency of each of the applications.
By the way, as a wide-band antenna system installed in a conventional portable radio apparatus, an antenna system of the configuration wherein a passive element is placed in the proximity of an antenna element is known (for example, refer to Patent Document 1). An antenna system of the configuration wherein a passive element connected to ground becoming a ground plate of an antenna element is placed in the proximity of the antenna element is also known (for example, refer to Patent Document 2).
In the antenna systems described above, the two elements of the antenna element and the passive element are used and high antenna performance can be ensured at the resonance frequency of each of the two elements and thus a wider band can be provided as compared with the case where the number of antenna elements is one.    Patent Document 1: JP-A-2005-20228    Patent Document 2: JP-A-2004-40154